Project Summary/Abstract The underuse of effective behavioral health treatments during the hospital stay is a translational science problem that has important consequences. Behavioral health comorbidities are common among hospitalized patients, and are associated with longer lengths of stay, higher costs and worse outcomes. Treatment for opioid use disorder (OUD) is an exemplar of this problem. Patients with OUD are frequently hospitalized, and while treatment is effective, it is dramatically underutilized, leaving patients at high-risk of continued misuse, future overdose, and readmission. There are multiple reasons for this translational inefficiency. While inpatient physicians frequently treat acute overdose and withdrawal, they have limited knowledge and training in behavioral health. Given pressures to minimize length of stay, the team usually prioritizes addressing the acute reason for admission. Moreover, few hospitals have the organizational infrastructure needed to treat behavioral health conditions effectively, such as dedicated teams, evidence-based protocols, or the ability to coordinate transitions of care such that patients can be linked to outpatient and community resources. Interdisciplinary, collaborative care teams (CCT) are a new approach to address translational roadblocks in OUD treatment delivery and have the potential to make a significant contribution to narrowing the treatment gap. Our prior work demonstrated the effectiveness of CCT when used with primary care patients with addiction, but CCT have never been tested as a translational approach in the inpatient setting. If effective, CCT could completely change the paradigm for addressing behavioral health disorders in the inpatient setting. We propose a mixed- methods, multi-site, randomized pragmatic trial in three sites to evaluate whether CCT increase translational efficiency, among hospitalized patients with OUD. We will randomize 414 patients total from Cedars Sinai Medical Center in Los Angeles, the University of New Mexico Hospital, and Baystate Health in Massachusetts to receive either CCT or usual care. Our primary outcomes are inpatient MAT initiation and linkage with post- discharge OUD treatment; secondary outcomes include days spent alive and in the community, treatment engagement, and opioid misuse. To inform future dissemination efforts, we also evaluate contextual factors affecting implementation, the sustainability of the CCT post-implementation, and costs. By blending components of clinical effectiveness and implementation research, leveraging the CTSA consortium including the Treatment Innovation Network and Recruitment Innovation Center, this innovative approach to translational research can generate more rapid translational gains, more effective downstream implementation, and will enhance the efficiency and science of translational research. The CCT offers expertise that most hospital-based physicians lack, creates an organized system of care, and addresses barriers to follow-up care. Knowledge from this study could transform the hospital experience into an opportunity to engage patients with OUD in MAT, resulting in reduced suffering, immediate and long-term gains in patient health, and decreased healthcare costs.